1. Field of the Invention
The present invention relates to a manufacturing method for an optical element that reflects, for example, a light beam thereon, to an optical element manufactured by the manufacturing method, and to an optical apparatus including the optical element.
2. Description of the Related Art
A technology of providing a positioning reference surface on an optical element and fixing the optical element to a holding member in order to accurately hold the optical element and to position a reference of an optical effective surface is disclosed in Japanese Patent Application Laid-Open No. H05-034553 and the like.
The optical element is frequently molded by injection molding of resin or the like because such injection molding using resin facilitates mass production of the optical element. However, with regard to the optical element fabricated by the injection molding, when a thickness of the optical element is reduced for the purpose of miniaturization thereof, a flow of the resin in a mold is deteriorated, and such deterioration adversely affects the optical effective surface in some cases. On the contrary, when the thickness of the optical element is ensured to some extent, such thickening inhibits the miniaturization. Further, an atmospheric temperature in an optical apparatus has gradually risen, and a shape of the optical surface is changed by deformation of the optical element owing to thermal expansion, causing a problem to deteriorate the optical performance of the optical element.
In recent years, in order to cope with the miniaturization of the optical element and to avoid the problem of the deformation due to the thermal expansion, such a technology as disclosed in Japanese Patent Publication No. H07-122120 has been researched. In this technology, amorphous metal as an amorphous material is used, and the optical element is molded thereof by press molding. The amorphous metal turns to a semi-molten state by being applied with heat up to a glass transition temperature thereof. The amorphous metal causes a viscous flow by being press-molded in this semi-molten state, and a shape of the mold can be accurately transferred thereto.
The amorphous metal has a higher Young's modulus than the resin has, and further, for the amorphous metal, it is not necessary to consider a flow of such a molding material in the mold as in the injection molding. Accordingly, the thickness of the optical element can be reduced more than in the injection molding of the resin, and the miniaturization of the optical element can be realized. Further, a linear expansion coefficient of the amorphous metal is smaller than that of the resin, and accordingly, even if the temperature in the optical apparatus rises, thermal expansion of the amorphous metal is small, and such deterioration of the optical performance owing to the thermal expansion is also small.
At the time of attaching the optical element to the optical apparatus or the like, it is necessary to provide a positioning reference on the optical element in order to position the optical element. However, a fabrication method for the positioning reference by the amorphous metal has not been disclosed yet.
FIG. 22A illustrates the case where a side surface portion 2 of a blank 1 before being press-molded is substantially parallel to an inner wall portion 4 of a mold 3, which is located in a direction in which the side surface portion 2 is pushed and extended, and a surface having high surface roughness is formed on the side surface portion 2 at a stage of fabricating the blank 1. The side surface portion 2 of the blank 1 is press-molded, whereby a surface shape thereof follows a shape of the mold as illustrated in FIG. 22B. However, an optical element having high surface roughness left thereon is formed.
As described above, when the optical element in which such a positioning reference portion is formed by a rough surface is fixed to the holding member, there arises a problem in that the optical element is undesirably inclined with respect to a design value. Further, when the side surface portion 2 of the blank 1 is polished before the blank 1 is press-molded, and the surface roughness is thereby improved, then secondary fabrication becomes required though the surface roughness of the positioning reference portion after the blank 1 is molded is improved. Accordingly, this way of improvement of the surface roughness by polishing is not desirable.